Reference

Bleuler, E. (1911/1950). Dementia praecox: Or the group of schizophrenias. New York: International Universities Press.

BLOCH'S LAW. See BUNSEN-ROSCOE LAW.

BLOCKING, PHENOMENON OR EFFECT OF. The phenomenon of blocking is an example in the psychology of learning and conditioning that the temporal contiguity alone between events is not sufficient for an association to be formed between them. Although the blocking effect was at one time claimed by selective attention theories, the American experimental psychologist Leon J. Kamin (1924- ) first described the blocking experiment where two groups of participants are used. One group is presented with a compound stimulus (called "AX") that is paired with an unconditioned stimulus (US), such as a noxious puff of air to the eye. A second group, before receiving an identical treatment, is given pretraining during which the "A" component of the compound stimulus is paired with the US (air puff). Following the "AX-US" pairing, the portion "X" of the compound stimulus is tested alone. It is found that "X" is more likely to elicit a conditioned response (CR), such as the eye blink, when the participants do not have prior training with the "A" component alone. The stimulus portion "X" of the compound stimulus is paired with the US (and, therefore, with the unconditioned response, UR) the same number of times in both groups. Contiguity between stimulus and response is established equally in both groups, and yet learning is not equal. The blocking phenomenon/effect indicates that there must be something more to conditioning and learning than mere stimulus-response contiguity. That is, if stimulus-response contiguity is a sufficient condition for learning to occur, then "X" should become an equally effective conditioned stimulus, or CS, in both groups, which it does not. Thus, blocking occurs when conditioning to a stimulus is attenuated, or "blocked," because that stimulus signals an outcome that was previously predicted by another stimulus or cue. Kamin's interpreta-

tion of the blocking effect is that conditioning depends on the predictability of reinforcement such that stimuli support learning only to the extent that the outcomes (that they signal) are "surprising." The first formal model to use Kamin's idea of "surprise" was developed by the American experimental psychologists Robert A. Rescorla (1940- ) and Allan R. Wagner. Their model differs from previous theories by assuming that the associative strength of a CS decreases over trials because the US becomes less effective when it is signaled by a stimulus with increasingly greater associative strength; thus, the US is reinforcing only to the extent that it is "surprising." Theories that have followed the Rescorla-Wagner model have been distinguished on the basis of whether they focus attention on the processing of the US or on the processing of the CS. The information-processing theory of A. Wagner (1978) focuses on the processing of the US; the attentional theory of N. Mackintosh (1975) and research by J. Pearce and G. Hall (1980) focus on the processing of the CS. However, none of the theories as yet developed can accommodate all of the observations made from the blocking experiments, even though they have stimulated much research in the field of learning/conditioning. See also ASSOCIATION, LAWS/PRINCIPLES OF; ATTENTION, LAWS, PRINCIPLES, AND THEORIES OF; INFORMATION AND INFORMATION-PROCESSING THEORIES; LEARNING THEORIES/LAWS; PAVLOV-IAN CONDITIONING PRINCIPLES/LAWS, AND THEORIES. REFERENCES

Kamin, L. J. (1968). "Attention-like" processes in classical conditioning. In M. Jones (Ed.), Miami symposium on the prediction of behavior. Miami, FL: University of Miami Press. Kamin, L. J. (1969). Predictability, surprise, attention, and conditioning. In B. Campbell & R. Church (Eds.), Punishment and aversive behavior. New York: Appleton-Century-Crofts. Rescorla, R. A., & Wagner, A. R. (1972). A theory of Pavlovian conditioning. Variations in the effectiveness of reinforcement and nonreinforcement. In A. Black & W. Prokasy (Eds.),

Classical conditioning. II. Current research and theory. New York: Appleton-Century-Crofts. Mackintosh, N. (1975). A theory of attention: Variations in the associability of stimuli with reinforcement. Psychological Review, 82, 276-298. Wagner, A. R. (1978). Expectancies and the priming of STM. In S. Hulse, H. Fowler, & W. Honig (Eds.), Cognitive processes in animal behavior. Hillsdale, NJ: Erlbaum. Pearce, J., & Hall, G. (1980). A model for Pavlovian learning: Variations in the effectiveness of conditioned but not of unconditioned stimuli. Psychological Review, 87, 532-552.

BLOCK'S CONTEXTUALISTIC MODEL OF TIME. The American cognitive and experimental psychologist Richard A. Block (1946- ) proposed a general contextualistic model of time which summarizes the interactions of four kinds of factors influencing psychological time and temporal experience: characteristics of the time experiencer; contents of the time period; the individual's activities during the time period; and the individual's time-related behaviors and judgments. Block acknowledges that although his approach clarifies many experimental findings and process-models of temporal experience, it does not yet provide the precise ways in which the four factors interact. See also FRASER'S INTERDISCIPLINARY TIME THEORY; ORNSTEIN'S THEORY OF TIME; PSYCHOLOGICAL TIME, MODELS OF; TIME, THEORIES OF. REFERENCES

Block, R. A., & Reed, M. (1978). Remembered duration: Evidence for a contextual change hypothesis. Journal of Experimental Psychology: Human Learning and Memory, 4, 656665.

Block, R. A. (1982). Temporal judgments and contextual change. Journal of Experimental Psychology: Learning, Memory, and Cognition, 8, 530-544. Block, R. A. (1989). A contextualistic view of time and mind. In J. T. Fraser (Ed.), Time and mind: Interdisciplinary is sues. Madison, CT: International Universities Press.

BLOOD-GLUCOSE THEORY. See HUNGER, THEORIES OF.

BLUE-ARC PHENOMENON. See VISION AND SIGHT, THEORIES OF.

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